The aim of this proposal is to critically analyze the immune mechanism whereby animals defend themselves against the parasitic nematode, Trichinella spiralis. Pursuant to this goal, the response of rats to phase-specific Trichinella antigens would be measured at the cellular level, correlations being drawn with the mechanism whereby antigen-activated cells or their products act alone or in concert to influence the biology of the parasite. Prominence would be given to the use of a adoptive transfer technique and "purified" populations of T and B cells obtained from the thoracic duct of Trichinella-infected donors. Experiments are planned to determine whether activated T cells act directly on the parasite or indirectly, by promoting the formation of protective antibodies. Affinity chromatography and antibody-mediated cytotoxicity would be used to characterize subpopulations of protective B cells with respect to the class of immunoglobulin determinants they express at the cell surface. Cells responsible for the production of protective antibodies would be quantified in gut-associated lymphoid tissue, the thoracic duct and the small intestine using monospecific antisera, purified antigens of preadult Trichinae and antigens of fully differentiated adult worms. Studies in both conventional and axenic rats are planned, correlations being drawn with the level of protective antibodies in the serum and intestinal lumen, and the capacity of the host to defend itself against an oral challenge infection with T. spiralis larvae. Finally, functional antigens of enteral stage Trichinae would be used in immunization protocols designed to stimulate the production of activated T cells, protective B cells or both.